Greening the city helps us breath more easily

Recent research on air pollution, published in the BMJ based on long-term data, links an increased risk of heart-attack for 100,000 people in five EU countries to exhaust pollution (see BBC News 22 Jan, 2014),The research focuses on so called PM 2.5 – particles smaller than 2.5 microns which are small enough to enter the blood stream across the lung membranes and move around the body.The BBC report cites wider evidence that perhaps 30,000 people die prematurely in the UK as a result of exposure to such emissions exacerbating a range of conditions including cancer, asthma and other lung problems as well as heart conditions.

Interestingly the emissions levels in the United States are more tightly regulated than in the EU. There new targets were set on 2007 to reduce the particle emissions by 75% in 2015 following evidence which included that diesel exhaust fumes posed a 7.5 times greater risk of cancer than all of the other airborne pollutants put together being monitored by the US Environmental Protection Agency. Here in the UK, while experts have stressed the risks to individuals is relatively small, and Defra spokesperson commented that emission levels have fallen significantly since EU emissions targets were set, the department’s report on the issue suggests their is no safe limit for PM 2.5.

Ironically a significant proportion of the particles of this size come from diesel vehicles, many of which are purchased because diesel is regarded as a ‘greener’ fuel. The problem lies in how vehicles are used in town and cities, particularly over short distances, If the engine is not hot then the exhaust gases do not heat the catalytic converters designed to remove these particles sufficiently for them to work efficiently. This is an issue because city driving behavior is hard to alter and improved technology comes at a price.

Interesting there is a more holistic, bio-diverse way to help mitigate the problem. Green Infrastructure (living plants) in cities can help manage the take up storm water and reduce urban heat; they can at the same time help address this pollution. A range of studies have confirmed how trees and plants in green walls alongside our urban roads can dramatically absorb car emissionpollutants, including PM 2.5. In 2012 Thomas Pugh and his colleagues reported in the ACS Journal of Environmental Science and Technology how green planting in cities could dramatically cut levels of PM 2.5 by as much as 60% – far more than had been previously believed. In 2013 the BBC participated in an experiment conducted by Barbara Maher and colleagues which was reported in the same journal. The researchers showed how planting sliver birch trees outside homes resulted in a drop by 50% of the particulate matter entering the home (the experiment measured overall amounts of PM10 – rather larger clusters of particles).The paper concluded that the potential of trees to mitigate particulate emissions was seriously underestimated.

Sadly in many areas the trend has been to plant smaller tree species which have more limited biodiversity and environmental benefits. These pieces of research point to how initiatives such as planting significant numbers of larger trees and encouraging the growth of green climbers, such as ivy, on the walls of buildings adjacent to roads could at low cost help create a significant asset in the fight to improve air quality in our urban spaces.